1. Field of the Invention
The invention relates to a control device and a control method for an internal combustion engine.
2. Description of the Related Art
Generally, a turbosupercharger-equipped engine has a problem of the back pressure becoming high in a high-speed and high-load operation region and therefore making it difficult to discharge the burned gas from the cylinders, so that the amount of gas remaining in the cylinders tends to be large. If the amount of residual gas in the cylinders becomes large, the combustion rate becomes slow and the in-cylinder temperature becomes high, so that knocking is likely to occur. Then, in order to avoid the knocking, it becomes necessary to perform an ignition timing retardation, which results in degraded fuel economy and reduced engine output. Besides, increases in the amount of residual gas correspondingly reduce the amount of air. Due to these circumstances, it is not easy to increase the output of the turbosupercharger-equipped engine in a high-rotation speed operation region.
In order to solve the problem as stated above, Japanese Patent Application Publication No. 10-89106 (JP-A-10-89106), for example, discloses an engine in which each cylinder is provided with a turbo-side exhaust valve that opens and closes an exhaust port that communicates with a turbo-side exhaust passageway that leads to a turbine inlet opening of the turbosupercharger, and with a bypass-side exhaust valve that opens and closes an exhaust port that communicates with a bypass-side exhaust passageway that does not lead to the turbine inlet opening.
Besides the problem of the difficulty in achieving high engine output in a high-speed operation region, the turbo-supercharger-equipped engines also have a problem of the catalyst warm-up at the time of startup of the engine requiring a long time. Furthermore, depending on the engine operation region, there is a problem of knocking or misfire being likely to occur, a problem of the required voltage of the ignition plug tending to become high due to heightened in-cylinder temperature, or the like.